Weegy:
Gas vents from Kilauea Volcano in Hawaii
Photo courtesy USGS
Magma Eruptions
Volcanoes vary a great deal in their destructive power. [ Some volcanoes explode violently, destroying everything in a mile radius within minutes, while other volcanoes seep out lava so slowly that you can safely walk all around them. The severity of the eruption depends mostly on the composition of the magma.
The first question to address is: why does the magma erupt at all? The erupting force generally comes from internal gas pressure. The material that forms magma contains a lot of dissolved gases - gases that have been suspended in the magma solution. The gases are kept in this dissolved state as long as the confining pressure of the surrounding rock is greater than the vapor pressure of the gas. When this balance shifts and vapor pressure becomes greater than the confining pressure, the dissolved gas is allowed to expand, and forms small gas bubbles, called vesicles, in the magma. This happens if one of two things occurs:
The confining pressure decreases, due to decompression from the magma rising from a higher pressure point to a lower pressure point.
The vapor pressure increases because the magma cools, initiating a crystallization process that enriches the gas content of the magma.
In either case, what you get is magma filled with tiny gas bubbles, which have a much lower density than the surrounding magma, and so push out to escape. This is the same thing that happens when you open a bottle of soda, particularly after shaking it up. When you decompress the soda (by opening the bottle), the tiny gas bubbles push out and escape. If you shake the bottle up first, the bubbles are all mixed up in the soda so they push a lot of the soda out with them. This is true for volcanoes as well. As the bubbles escape, they push the magma out, causing a spewing eruption. the answer is a.
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Weegy: Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers. [ [ [ Eventually some of the magma pushes through vents and fissures in the Earth's surface. A volcanic eruption occurs! Magma that has erupted is called lava.
Some volcanic eruptions are explosive and others are not. How explosive an eruption is depends on how runny or sticky the magma is. If magma is thin and runny, gases can escape easily from it. When this type of magma erupts, it flows out of the volcano. Lava flows rarely kill people, because they move slowly enough for people to get out of their way. Lava flows, however, can cause considerable destruction to buildings in their path.
If magma is thick and sticky, gases cannot escape easily. Pressure builds up until the gases escape violently and explode. In this type of eruption, the magma blasts into the air and breaks apart into pieces called tephra. Tephra can range in size from tiny ] ] ] (More)